This disclosure relates to the concentration or collection of light, and, more particularly, the concentration or collection of light using an optical element.
Typically, light concentrators operate to receive light incident over a range of angles less than an acceptance angle at an aperture. The light is concentrated onto a region (e.g. on an absorber) with an area smaller than the area of the aperture. The ratio of the aperture area to the smaller area is known as the geometric concentration C. The laws of thermodynamics set a theoretical upper bound, known in the art as the “thermodynamic limit,” to the concentration for a given concentrator configuration.
Many types of solar concentrators have been studied including reflective and refractive devices. Concentrators may be imaging or non-imaging, and may be designed to correct for various types of optical aberration (spherical aberration, coma, astigmatism, chromatic aberration, etc.). For example, D. Lyndon-Bell, Monthly Notices of the Royal astronomical Society, vol. 334, pp. 787-796 (2002), describes an aplanatic concentrator featuring primary and secondary reflectors. However, the efficiency of such concentrators is limited by the obscuration of the primary reflector by the secondary reflector.
Optical concentrators may be applied, for example, in the conversion of solar energy to electricity (or other form of energy). The power that a photovoltaic solar cell can produce is a function of the incident sunlight. A typical solar cell can utilize efficiently many times the un-concentrated incident sunlight in typical settings, provided that the temperature of the solar cell does not increase excessively. Therefore, an optical concentrator can be employed to concentrate sunlight onto a photovoltaic cell to improve the output of the photovoltaic cell. The output will increase with the concentration factor. At appreciable concentration factors, cooling may be required, since the efficiency of some photovoltaic cells may decrease rapidly with increasing temperatures.
Optical concentrators may be applied in a variety of other applications including, for example, imaging, photography, concentration of light from sources such as lasers or light emitting diodes (LEDs), etc.